I just got one of my 2003 Exmark TTHP's out of the shop. It was fixed under Kawi warranty for surging and running very poorly. They had to tear down the engine and replace some parts. It is running good now. The mechanic told me there was alot of dirt inside the engine and said it was due to using aftermarket filters. He said they make look the same as OEM but are NOT the same. What do you guys think?